How many vertebrae in human spine

Between the vertebrae are pads called the intervertebral discs. A disc is made of an outer ring called the annulus and fluid-filled centre called the nucleus. With age, our discs increasingly lose the ability to reabsorb fluid and become brittle and flatter. This is why we get shorter as we grow older. Injuries such as back strain can cause discs to herniate. A herniated disk is a condition that can occur anywhere along the spine, but most often occurs in the low back.

It is one of the most common causes of low back pain. The length of the spinal cord is approximately 45 cm in men and 43 cm in women. The diameter ranges from 13 mm in the cervical and lumbar regions to 6. The cord is protected within the spinal canal and runs from the brainstem to the lumbar area where the cord fibres separate.

The fibres then continue down through the canal to the sacrum and coccyx where they branch off to legs. The spinal nerves act as phone lines carrying messages back and forth between the body and spinal cord to control sensation and movement.

The spinal cord serves as an information highway, relaying messages between the brain and the body. Damage to the spinal cord may result in a loss of sensory and motor function below the level of injury. Back muscles stabilize the spine and support proper alignment of the vertebrae. The three types of back muscles that help the spine function are extensors, flexors and obliques:. Facet joints make the spine flexible and enable us to bend and twist. Each vertebra has four facet joints, one pair that connects to the vertebra above and one below.

There are three main ligaments which run from the top to the bottom of the spine the anterior and posterior longitudinal ligaments and the ligamentum flavum , as well as further ligaments joining adjacent vertebrae such as the interspinous ligaments.

As part of the degenerative process, ligaments can become enlarged or lengthened, and this can also contribute to the development of spinal stenosis or myelopathy.

The neurological part of the spine consists of the spinal cord and the nerves emerging from it the spinal nerves. These are contained deep within the centre of the spine in the canal formed by bony arches of each vertebra. The enveloping bone and ligaments means that the neurological structures are exceedingly well protected.

The spinal cord emerges from the brain cavity where it is continuous with the lower brainstem. The spinal cord carries a vast amount of information both to and from the trunk and limbs. The motor messages run from the brain downwards, and sensory signals originate peripherally and are then relayed back to the brain via the spinal cord. Considering the number and speed of the electrical messages conveyed, the spinal cord is a remarkably small structure only measuring approximately mm in maximum diameter.

The spinal cord is enveloped in a number of protective coverings called the meninges. The outer layer is the dura, which is the thickest and toughest membrane. Within the dura there are two much thinner membranes called the arachnoid and pia. There is a narrow space between the dura and the bone and ligaments of the spine, and this is called the epidural space. It is this space that is targeted for steroid or anaesthetic injections. On the inside of the arachnoid membrane, a clear watery fluid called cerebrospinal fluid CSF bathes the spinal cord.

A lumbar puncture accesses CSF from this space, and a contrast dye can be injected into it when obtaining a CT myelogram. Emerging from the spinal cord are 31 pairs of spinal nerves 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal.

The coccyx is at the very base of the spinal column and is made of four vertebrae that are fused together. The spine is normally a straight line when viewed from the back. If the spine curves to one side or the other, this indicates a condition named scoliosis. However, the spine does have some normal, gradual curves when viewed from the side.

The neck and lumbar sections of the spine have a lordotic curve, which means that they curve inward. These spinal curves help maintain balance while upright and support the weight of the head and upper body. However, too much curvature may cause spinal imbalance, causing spinal conditions that may result in pain or loss of mobility. Normal adult spines are positioned over the pelvis, so upright posture doesn't strain muscles.

However, changes of spinal position can stress muscles and cause spinal deformity. If the spine is injured and unable to function properly, it can be very painful or even disabling. The spine is made of many parts that protect the spinal cord, facilitate movement and support the body. The spinal cord has nerve pathways that carry signals, such as pain, from the arms, legs, and the body to the brain.

Nerve roots are used to transmit information between the spinal cord and the other parts of the body, such as arms, legs and organs.

The flat plates of the lamina create the outer wall of the vertebral canal and help protect the spinal cord. The three major ligaments of the spine are the ligamentum flavum, anterior longitudinal ligament ALL , and posterior longitudinal ligament PLL Fig.

The ALL and PLL are continuous bands that run from the top to the bottom of the spinal column along the vertebral bodies. They prevent excessive movement of the vertebral bones. The ligamentum flavum attaches between the lamina of each vertebra.

The spinal cord is about 18 inches long and is the thickness of your thumb. It runs from the brainstem to the 1st lumbar vertebra protected within the spinal canal. At the end of the spinal cord, the cord fibers separate into the cauda equina and continue down through the spinal canal to your tailbone before branching off to your legs and feet.

The spinal cord serves as an information super-highway, relaying messages between the brain and the body. The brain sends motor messages to the limbs and body through the spinal cord allowing for movement.

The limbs and body send sensory messages to the brain through the spinal cord about what we feel and touch. Sometimes the spinal cord can react without sending information to the brain. These special pathways, called spinal reflexes, are designed to immediately protect our body from harm.

Any damage to the spinal cord can result in a loss of sensory and motor function below the level of injury. For example, an injury to the thoracic or lumbar area may cause motor and sensory loss of the legs and trunk called paraplegia. An injury to the cervical neck area may cause sensory and motor loss of the arms and legs called tetraplegia, formerly known as quadriplegia.

Thirty-one pairs of spinal nerves branch off the spinal cord. Each spinal nerve has two roots Fig. The ventral front root carries motor impulses from the brain and the dorsal back root carries sensory impulses to the brain.

The ventral and dorsal roots fuse together to form a spinal nerve, which travels down the spinal canal, alongside the cord, until it reaches its exit hole - the intervertebral foramen Fig.

Once the nerve passes through the intervertebral foramen, it branches; each branch has both motor and sensory fibers. The smaller branch called the posterior primary ramus turns posteriorly to supply the skin and muscles of the back of the body.

The larger branch called the anterior primary ramus turns anteriorly to supply the skin and muscles of the front of the body and forms most of the major nerves.

The spinal nerves are numbered according to the vertebrae above which it exits the spinal canal. The 8 cervical spinal nerves are C1 through C8, the 12 thoracic spinal nerves are T1 through T12, the 5 lumbar spinal nerves are L1 through L5, and the 5 sacral spinal nerves are S1 through S5. There is 1 coccygeal nerve. The spinal nerves innervate specific areas and form a striped pattern across the body called dermatomes Fig.

Doctors use this pattern to diagnose the location of a spinal problem based on the area of pain or muscle weakness. For example leg pain sciatica usually indicates a problem near the L4-S3 nerves.